A number of catheter assemblies are known which utilize a relatively long flexible hollow plastic cannula for insertion into the vein of a patient for the infusion of intravenous fluids including nutrients and/or medication. Generally, one end of the cannula is attached to the hub and a steel needle which is sized to fit within the duct of the cannula is inserted into the hub from the side opposite the attachment of the cannula sufficiently so that the steel needle exits the cannula at its distal end. The needle is then inserted into the vein of a patient after which it is removed from the cannula and the hub, leaving the cannula behind with its distal end in the vein. An intravenous feeding and/or medication tube is then attached to the hub whereby flow can take place through the hub and the cannula and into the vein.
Catheter assemblies are also used for other purposes, for example, for endotracheal tubes, and the like. Also, the cannula of such assemblies can be inserted by over the needle and through the needle techniques and, in the case of endotracheal tubes or the like, without the use of a needle.
The cannulae of the prior art have generally been made of a rigid material which does not change the cross-sectional area of the duct of the cannula after insertion into a vein. More recently, as set forth in commonly assigned co-pending U.S. patent application Ser. No. 780,543 filed Sept. 26, 1985, materials have been developed which can be formulated into cannulae and which, while they are rigid enough to retain their shape during insertion, also, have the property of swelling to form an enlarged duct cross-section, due to water pickup. Also, recent publications discuss cannulae which, on being raised to a temperature approaching body temperature undergo a shape change motivated by plastic memory, to form somewhat shorter, larger duct cross-section cannulae.
If such increasing duct cross-section cannulae as are discussed above are attached to the conventional hubs of the prior art the full effect of the increased duct cross-section, in flow rate, cannot be realized because prior art hubs are such that flow will be limited either because of the size of the passageway through the hubs or because the hubs hold the cannulae in such a manner that instead of the cannulae proximal ends being held so that the duct cross-section can increase, the cannulae are externally restrained whereby the duct cross-section is forced to decrease.
The present invention is directed to overcoming one or more of the problems as set forth above.